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THE

POPULAR SCIENCE

MONTHLY.

MAY, 1880.

CLIMATE AND COMPLEXION.*

BY J. M. BUCHAN, M. A.

T
WHERE is a great diversity of opinion as to the reason of the dif-

ferences of complexion to be observed among mankind. Roughly speaking, the hue of the skin varies with the latitude, the fairer races having their homes at a distance from the equator ; the darker, within or near the tropics. This fact would seem to point to the position of the sun with reference to those on whom he shines as the cause. But the question presents difficulties which this supposition does not aid us to solve.

At the same distance from the equator we find the fair Englishman, the yellow Mongol, and the copper-colored Indian. To the north of the white Russian and Finn live the swarthy Lapp and Samoyed. North of the Caucasus are dark-skinned Tartars, south of it fair-complexioned Circassians. The aborigines of America vary less in color than the natives of the Old World. None of them are as fair as the Swede, none as black as the negro of Congo, and those living in Brazil on the equator are not the darkest. There are blacker men in Australia and New Guinea than in Borneo and Sumatra, though these islands are on the equator and those are not. The Shillooks of the Upper Nile, who live about 10° north latitude, are blacker than the Monbuttoo who are six degrees farther south.

Many attempts have been made to explain these and similar facts. It has been asserted that mountaineers are fairer than lowlanders in the same latitude. This is generally the case, but there are some striking exceptions to the rule. The natives of the Mexican plateaus are as brown as those of the coast, and the Aymaras and Quichuas of

This paper embodies the substance of a communication made to the Canadian Institate, Toronto, at a recent meeting.

VOL. XVII.-1

the Peruvian Andes are darker than the Yuracaras of the forests to the east. The inhabitants of the Altai Mountains are yellow ; those of the plains of European Russia, at the same distance from the equator, white. According to Foissac, the blackness of the negro is a consequence of his vegetable diet, by which his blood is overloaded with carbon. But this theory, likewise, breaks down when submitted to the test of a comparison with the facts. The nomads of the Asiatic deserts, who live mainly on milk and flesh, are certainly not fairer than the grain-eating peasants whom they plunder ; and the Buddhists of China and Japan, whose religion prohibits the use of animal food, do not differ in color from their neighbors of other creeds. The influence of humidity has attracted the attention of some writers. Sir R. Schomburgk and M. d'Orbigny hold that it tends to lighten, Dr. Livingstone and others that it tends to darken, the hue. I shall state below my reasons for agreeing with the former.

Mr. Charles Darwin, Professor Huxley, M. Quatrefages, and others, think it probable that racial distinctions owe their origin to the selective operation of the prevailing diseases of particular climates. Assuming, what is amply supported by facts, that individuals slightly diverging in various directions from the type are constantly being produced, it is obvious that if a dark or a light complexion be correlated with power to resist a particular disease, or group of diseases, a white race may, by natural selection, be gradually developed from a colored one, or vice versa. M. Quatrefages has suggested that the malarial fevers of Africa have wrought this effect there, and that phthisis has been the agent in the north of Europe. It certainly is the case that the tropical regions of Africa are very unhealthy for whites, and that the negro dies out north of the parallel of 40° in both hemispheres ; but this does not show that both races might not be acclimatized by slow degrees without loss of color. In other words, no reason has been shown for thinking that it is to the complexion and not to some other racial peculiarity that the relative immunity from certain maladies is due. To connect the color with this immunity is the object of this paper.

I may say at the outset that I do not attach much importance to the direct influence of climatic conditions. It is, indeed, a matter of common observation that these produce considerable effects on the individual. Pruner, for example, states that he has noticed that the European acclimated in Egypt acquires after some time a tawny skin, and in Abyssinia a bronzed skin; he becomes pallid on the coast of Arabia, cachectic white in Syria, clear brown in the deserts of Arabia, and ruddy in the Syrian mountains."* But there is no proof that these cutaneous changes are inherited. If, however, it can be shown that a particular kind of skin is better than others for withstanding certain obvious weakening influences of a given climate, it stands to

Waitz, “ Anthropology."

reason that those members of a race whose skins vary in the direction of this type will in each generation have the best chance of surviving and begetting children, and that, by the continued increment of successive variations in the same direction, the skin and the climate will ultimately be brought into accord.

The skin consists of two layers : the inner, dense and fibrous, furnished with blood-vessels and nerves, called the dermis, or true skin ; the outer, horny, nerveless, and bloodless, called the epidermis, cuticle, or scarf-skin. The cells which compose the latter originate in the rete Malpighii, its lowest part, are gradually forced outward by new cells, and finally exfoliate. In some of these epidermic cells a pigment is found which varies in different races, but always contains a yellow element. The hue of the skin does not depend on this coloring matter alone, but is a compound effect, resulting from the white of the dermis, the red of the blood in the minute vessels near the surface, the color and quantity of the pigment, and the thickness of the cuticle. Where the cuticle is thick, the color of the pigment will predominate over the other elements on account of the greater depth of pigment-cells. Where it is thin, and the coloring matter light, the tint of the skin will be much affected by any change in the supply of blood to the capillaries at the surface of the body. This is the reason why the whites alone can turn pale and blush.

Closely related to the pigment of the skin are the coloring matters of the eye and hair. Dark-skinned people usually have black eyes and bair ; fair hair and blue eyes are seldom found except in conjunction with a fair skin ; and the eyes and hair of albinoes, in whom the pigment of the skin is wanting, are likewise destitute of coloring matter. The pink hue of their eyes is due to minute blood-vessels, whose color is masked in ordinary organs by the pigment of the iris.

It is noteworthy that the coloring matters of the epidermis and iris serve a very important purpose : they protect the tender underlying parts from the injurious effects of too much heat and light. Albinoes everywhere find it necessary to protect their skins and eyes from the effects of the sun's rays. In warm countries they seldom go out except at night. There is this difference between them and other men, that long-continued exposure to the sun, which ordinarily develops a condition of the skin capable of resisting its rays, does not do so in their case. It may here be remarked that the deeper the shade of the pigment, the more rays will it reflect, and the more effective will it be as a protective agency. On the contrary, the lighter the shade, the more light and heat will it permit to enter the body.

As an excretory organ, it is the function of the skin to discharge water, carbonic acid, and urea-the first in large, the others in small quantities. Perspiration, or the excreting of water, with some saline matter in solution, is effected in two ways: In the first place, sudoriparous glands, imbedded in the true skin, secrete sweat from the blood. This is conveyed to the air by minute ducts passing through the epidermis. It is obvious that, the blacker the pigment, the less light and heat will be transmitted to excite these glands into activity. In the second place, there is a continual transudation of sweat from the minute vessels of the surface of the body through the epidermis at every point. The thicker or the more oily the scarf-skin, the less will the amount of this transudation be. If it be both thick and oily, as in many

dark

races, the quantity transuded will be reduced to a minimum; if it be thin and not oily, as in the fairest members of the white race, transudation will be copious.

The amount of transuded sweat depends, however, not merely on the thinness of the cuticle, but also on the degree to which the air in contact with the body is saturated with moisture ; for there is a limit to the quantity of vapor which the air can absorb. This limit varies with the temperature, warm air absorbing more than cold. Such being the nature of the skin, I now proceed to inquire what kind of it will best suit particular regions. For this purpose climates may be classified as

I. Arctic.
II. Temperate humid.
III. Temperate dry.
IV. Tropical humid.

V. Tropical dry.

I. When the skin is exposed to great cold, perspiration by transudation is accelerated. The frosty air, raised many degrees in temperature by contact with the body, becomes very dry, and greedily drinks in its moisture. At the same time the body loses, not only the heat which the air carries off, but also that which is rendered latent by the evaporation of the sweat. As a protection against the injury which a too rapid loss of perspiration and heat may inflict in an arctic climate, a thick integument is desirable. On account of the obliquity of the sun's rays a dark pigment will be a disadvantage, because it will prevent the passage of light and heat. Some pigment will, however, be needed, as not even in northern regions can albinoes expose themselves to sunlight with comfort. The coloring matter, then, will be light; but, owing to the thickness of the cuticle, the general effect will be yellow.

II. By a humid temperate climate I mean one occurring in a temperate zone, in which the air constantly contains a large amount of moisture. Humidity does not to any considerable extent depend on the amount of the annual rainfall. The annual rainfall of London is twenty and one half inches, that of Toronto thirty inches ; yet the air of the former place is incomparably more humid. Countries in which this climate is found are distinguished from others in the same latitude by the limited range of the thermometer. This is due partly to the fact that water can not be so rapidly heated as air, and partly to the

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